1. Field of the Invention
The invention relates to a sprung mass damping control system of a vehicle, which suppresses sprung mass vibration generated in a body of a vehicle provided with at least a motor-generator as a drive source.
2. Description of the Related Art
Technology referred to as sprung mass damping control that suppresses sprung mass vibration generated in a vehicle body using predetermined vibration damping means is well known. For example, Japanese Patent Application Publication No. 2004-168148 (JP-A-2004-168148) and Japanese Patent Application Publication No. 2006-69472 (JP-A-2006-69472) describe technologies that control the driving force of a vehicle in order to suppress sprung mass vibration in the vehicle. In the technologies described in JP-A-2004-168148 and JP-A-2006-69472, the driving force is controlled by increasing or decreasing the engine torque. To perform this control, these technologies increase or decrease the engine torque as necessary by adjusting the intake air amount, the fuel injection amount, and the ignition timing and the like of the engine.
However, the states of the air and fuel that are supplied to the engine are not always constant. For example, the temperature and humidity of the air changes according to changes in the ambient air temperature and the altitude and the like. Also, with commercially available fuel, there are different types of a given gasoline fuel which differ from one another in terms of their octane numbers, for example, and even with the same type of gasoline fuel, there may be different compositions due to differences in additives and impurities. Furthermore, some engines may be able to use either a gasoline fuel or an alcohol blend, for example. Therefore, the fuel stored in the fuel tank of the vehicle may not necessarily be homogenous fuel. If air of a different temperature or a different type of fuel are supplied, for example, the engine torque that is output will change compared with a case in which air and fuel of given reference states are supplied, even if all of the other conditions are the same. Also, if the air pressure changes due to a change in altitude or the like, the intake air amount will change. Therefore, in this case as well, there will be a difference in the engine torque that is output, even if the other conditions are the same. Moreover, engines have poorer responsiveness for generating the required torque (i.e., engine torque) than motors do. Therefore, the control precision of sprung mass damping control may decease if engine torque is used.